Such a front jaw is already described in AT-PS 321 170 (corresponding to U.S. Pat. No. 3 902 730). However, this front jaw has the disadvantage that the release spring is only slightly compressed during a backward twisting fall and thus the work to be done by the swinging-out toggle lever is reduced. During a forward fall, combined with a twisting fall, the release spring did not compress.
In a front jaw with laterally spaced toggle levers, the measure of increasing the initial tension of the release spring during a combined frontal and twisting fall and thus reducing the work to be done during a swinging out of one toggle lever, is already known as shown by DE-PS 2 905 837 (corresponding to U.S. Pat. No. 4 336 956). However, the effect occurs here only during a frontal fall and not also during a backward fall, which is combined with a twisting fall.
In a front jaw according to AT-PS 372 616, the shorter arms of the two toggle levers are supported on a bifurcated intermediate lever. The horizontal arm of the intermediate lever is thereby loaded by a separate sole down-holding means, which is arranged on a vertical locking bolt. Same is supported elevationally movably in a guideway in the base plate. Furthermore, the path of movement of the locking bolt is limited because of the design (compare AT-PS 372 616).
The purpose of the invention is to overcome the disadvantages of the known designs and to provide a particularly simple solution with which an initial tension of the release spring occurs during a forward fall and during a backward fall, which falls can be combined with a twisting fall.